The distance a bird flies

Two trains, each having a speed of $$30 \text{ km/h},$$ are headed at each other on the same straight track. A bird that can fly $$60 \text{ km/h}$$ flies off the front of one train when they are $$60 \text{ km}$$ apart and heads directly for the other train. On reaching the other train, the bird flies directly back to the first train, and so forth. What is the total distance the bird travels before the two trains collide?

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